Colicin U

Colicin U is a type of Colicin, a bacteriocin made by E. coli which acts against other nearby E. coli to kill them through Pore Formation, leading to depolarisation of the membrane which kills the cell.

Synthesis and release
The operon encoding Colicin U is encoded on a plasmid, in the cytoplasm of the E. coli. The operon also encodes its Colicin Immunity Protein, Cui, and a protein that enables the release of the colicin from the producing cell.

The immunity protein inserts into the membrane of the colicin-producing cell to prevent the colicin from inserting into the membrane, and therefore protecting the cell from the colicin's killing activities.

Mechanism of uptake
The receptor binding domain of the colicin binds to an outer membrane receptor, as yet unidentified. The translocation domain then recruits proteins from the Tol system to translocate the colicin across the membrane. This mechanism is also so far unidentified.

Killing Activities
Colicin U kills its target cell by Pore Formation; it inserts into the membrane of the cell and forms a pore. This leads to depolarisation of the membrane, which prevents the synthesis of ATP, ultimately leading to the death of the cell.